The invention relates to electromagnetic actuators, particularly for use with valves in the automotive field, such as, exhaust-gas recirculation valves, secondary-air valves, etc. The electromagnetic actuator has a housing with an electrical connector plug, a magnetic yoke, a coil unit, a guide element, a magnetic core and an armature, which cooperates with a valve actuator.
Such an actuator is disclosed in DE-A1-198 31 140 combined with an exhaust-gas recirculation valve. A cylindrical armature acts as a linear magnet, to move the valve closing member into an open position of the exhaust-gas recirculation valve, by means of a valve actuator that cooperates therewith, when current is supplied to the coil unit. When the current supply to the coil unit ceases, the valve closing member moves back to a closed position of the exhaust-gas recirculation valve by means of a spring, which acts on the valve actuator.
In particular, in valves in the automotive field, such as, exhaust-gas recirculation valves, secondary-air valves and the like, there may occur gumming or freezing, etc. of the valve closing member due to the high thermal loads, as well as due to environmental influences. The valve then can no longer be opened and its function is no longer assured. In most cases this requires an expensive repair or replacement of the valve.
An object of the invention is to provide a valve actuator which avoids the problem described above.
This object is achieved according to the invention in that the armature is comprised of first and second armature elements and wherein the second armature element is formed as a disk and when current is not supplied to the actuator, the disk is spaced from the first armature element by an air gap.
In this way, the second armature element acts as a plate magnet when current is supplied to the coil unit, and the plate magnet applies an abrupt pull on the first armature element and in this way produces a substantially increased opening force on the valve closing member. When the first armature element is pulled against the second armature element, both armature elements act together as a single armature similar to the linear magnet, which opens the valve closing member in the conventional way. Thus, the same function can be assured with a smaller coil. It has been found particularly advantageous that when the coil unit, the magnetic core and armature elements are appropriately designed, the air gap is between 0.1 mm and 2.0 mm. A particularly simple construction of the electromagnetic actuator is obtained if the valve actuator is secured to the first armature element in a form-fitting or frictional manner. A sleeve is secured to the second armature element in a form-fitting or frictional manner and is mounted so that it can move in the magnetic core, the valve actuator being displaceable in the sleeve whereby a particularly simple and compact construction of the electromagnetic actuator is obtained. The sleeve has a projecting end, which is applied against the underside of the magnetic core in an initial position of the second armature element when current is not supplied to the coil unit.
It has also proven advantageous if the end of the valve actuator terminates at the projecting end of the sleeve or projects slightly beyond it in order to assure opening of the valve closing member with a small stroke of the valve actuator. In order to assure proper guiding of the armature and the necessary magnetic isolation, a bearing bush is arranged both in the guide element and in the magnetic core for respective movable mounting of the first and second armature elements while providing the magnetic isolation between the armature elements.
The invention is also directed to the combination of a valve with the electromagnetic actuator, wherein a valve adjusting member of the actuator cooperates with the valve closing member which is guided in a valve housing, the valve closing member being joined, in turn, with a sleeve element by means of a coupling. A restoring spring acts on the coupling and is supported in the valve housing such that the valve adjusting member, the valve closing member and the sleeve element are biassed to close the valve when current is not supplied to the coil unit.